A press roll, which presses a web at a nipping portion formed between the roll and a counter roll, is employed, for example, in the press section of a paper making machine to dewater the web. As shown in FIGS. 19 and 20, the structure disclosed in Japanese Patent Publication No. HEI 3-41586 is known as a conventional press roll for a papermaking machine. FIG. 19 is a vertical sectional view of the principal part of the conventional press roll, and shows a view taken in the direction of arrow H in FIG. 20.
As shown in FIG. 19, the press roll includes a counter roll 44, a supporting body 42 disposed to face the counter roll 44, and a supporting disc 31 rotatably supported by the supporting body 42. The press roll further includes a flexible blanket 30 whose end portion is mounted on the supporting disc 31, a flange 32 for clamping the blanket 30 to the supporting disc 31 in the axially inward direction of the press roll, and a sliding mechanism 51 for sliding the supporting disc 31 in the axial direction.
The supporting body 42 is disposed under the counter roll 44 and extends in the same axial direction as the counter roll 44. The axially central portion of the supporting body 42 is provided with a groove 50 in which a piston (not shown) is fitted so that it is movable in the radial direction of the supporting body 42.
Furthermore, the tip end of the piston is provided with a press shoe 43. The exterior surface of the press shoe 43 has a concave shape. The radius of curvature of the press shoe 43 is set so that a small gap is formed between the press shoe 43 and the outer peripheral surface of the large-diameter portion of the counter roll 44 facing the press shoe 43. If pressurized oil is supplied to the groove 50, the press shoe 43 is pressed through the piston against the outer peripheral surface of the counter roll 44 via the blanket 30.
Ring-shaped sleeves 46 are fitted on the axially opposite end portions (in FIG. 19, only one end is shown) of the supporting body 42 so that they are slidable in the axial direction. The blanket-supporting disc 31 is supported on the outer periphery of each sleeve 46 through a bearing 45 so that it is rotatable in the circumferential direction. A bearing pedestal 49 is mounted on one end of the supporting body 42. The sleeve 46 is slidable in the axially inward direction of the press roll by a screw 48 inserted into the bearing pedestal 49, and is also slidable in the axially outward direction by the reaction force of a spring interposed between the sleeve 46 and the supporting body 42.
The cylindrical flexible blanket 30 is mounted at its axial end portions on the blanket-supporting discs 31. The axially opposite end portions (in FIG. 19, only one end portion is shown) of the blanket 30 have tongue portions 36 of uniform length, required for mounting over the circumference of the supporting disc 31. The tip end of each tongue portion 36 is provided with a bore 37 of suitable size. The bottom portion of a cutout between two adjacent tongue portions 36 has a suitable radius of curvature. The end portion of the blanket 30 is bent at a right angle along the outer end surface of the blanket-supporting disc 31. The blanket 30 is positioned by bushes 41 and pins 33, 38 provided in the outer end surface of the blanket-supporting disc 31 and is clamped by a clamping flange 32 and mounting bolts 34 (details of the mounting method will be described later). Therefore, in combination with an O-ring 40 provided in the axially outer end surface of the blanket-supporting disc 31, lubricating oil between the concave area of the press shoe 43 and the inner surface of the blanket 30 is prevented from leaking to the outside. In the state in which the blanket 30 is rotatably supported by the supporting body 42, the blanket 30 is moved in the axially outward direction by applying a suitable force to the sleeve 46 with spring 47.
In this state, if the counter roll 44 is rotated by a drive unit (not shown), the blanket 30 rotates while being lubricated along the concave surface of the press shoe 43.
In the press roll for dewatering a web, if an endless rotating felt and a web are inserted between the blanket 30 and the counter roll 44, the web is pressed against the press shoe 43 and therefore moisture in the web is transferred to the felt. As a result, the web is dewatered. The dewatered web is separated from the felt and moved to the dryer section, the calender section and the reel section.
As described above, the blanket 30 is inserted between the press shoe 43 and the counter roll 44 during operation and repeatedly undergoes bending, stretching, and compression. Because of this, the blanket 30 is liable to be damaged, and must be frequently exchanged in a relatively short period.
However, when exchanging the blanket 30, the press roll has to be stopped. Therefore, in order to obtain a high rate of operation, it is necessary to reduce the number of exchanges of the blanket 30 and to exchange the blanket 30 in a short time.
Next, based on the aforementioned Japanese Patent Publication No. HEI 3-41586, a description will be given of how a new blanket 30 is mounted on the blanket-supporting disc 31 when the conventional blanket 30 is exchanged.
FIG. 20 is a diagram (taken in the direction of arrow G in FIG. 19) showing the state in which the conventional blanket 30 is mounted on the blanket-supporting disc 31. In the outer end surface of the supporting disc 31, the bushes 41 and pins 38 corresponding in number to the cutouts 35 are disposed at equal intervals on a concentric circle smaller than the outside diameter of the supporting disc 31. On an even smaller concentric circle, the pins 33, equal in number to the tongue portions 36, are disposed at equal intervals.
When a new blanket 30 is mounted on the supporting disc 31, the screw 48 is first tightened to move the sleeve 46 and the supporting disc 31 in the axially inward direction. Then, as shown in FIG. 19, the end portion of the blanket 30 is bent at a right angle to bring the bottom portions 35a of the cutouts 35 into contact with the bushes 41 and the pins 38. At the same time, the bores 37 of the tongue portions 36 are fitted on the pins 33 to perform positioning of the end portion of the blanket 30.
A sequence of these operations is performed on all of the tongue portions 36 of both ends of the blanket 30. Thereafter, as shown in FIG. 19, the blanket 30 is fixed to the supporting disc 31 by clamping the clamping flange 32 with the mounting bolts 34. Finally, the screw 48 is loosened to move the supporting disc 31 in the axially outward direction. In this way, all operations are completed.
If the blanket 30 has a twist when it is mounted on the supporting disc 31, or the blanket 30 is eccentrically mounted on the supporting disc 31, good rotation cannot be obtained during operation and the quality of the web will degrade. Therefore, the blanket 30 must be stretched uniformly and mounted on the supporting disc 31 without eccentricity. Because of this, in the state in which phases in the direction of rotation coincide at both ends of the blanket 30 (a state in which there is no twist with respect to the axis of rotation), the blanket 30 needs to be mounted on the supporting disc 31 without eccentricity. Hence, the bores 37 of the tongue portions 36 of both ends of the blanket 30 need to be fitted on predetermined pins 33.
However, even if the bores 37 are fitted on the pins 33 at correct positions, a twist will occur partially in the blanket 30 if some of the tongue portions 36 of the blanket 30 are positioned in directions inclined from the radial direction of the supporting disc 31. In the partially twisted state, if the blanket 30 is fixed with the clamping flange 32 and is stretched in the axially outward direction, undulations will occur in the blanket 30. For this reason, the tongue portions 36 need to be positioned with respect to the supporting disc 31 without being inclined before the clamping flange 32 is clamped.
In this conventional method, the bottom portions 35a of the cutouts 35 are merely brought into contact with some of the bushes 41 and pins 38. Therefore, if the length from the bore 37 of the tip end of the tongue portion 36 to the center of curvature of the bottom portion 35a of the cutout 35 is longer than the distance between the pin 33 and the bush 41 (or the pin 38), there is a possibility that the bottom portion 35a of the cutout 35 cannot abut the bush and therefore the tongue portion 36 will incline. Because of this, the length from the bore 37 of the tip end of the tongue portion 36 to the center of curvature of the bottom portion 35a of the cutout 35 is made shorter than the distance between the pin 33 and the bush 41 (or the pin 38), and the tongue portions 36 are tensioned and attached to the supporting disc 31.
In a sequence of operations of tensioning the tongue portions 36 and fixing the blanket 30, as shown in FIG. 21, a tool 39 is first passed through the bore 37 of the tongue portion 36 and connected to the pin 33.
Then, the tool 39 is rotated toward the center axis of the supporting disc 31 to bring the bottom portion 35a of the cutouts 35 into contact with the bush 41 and the pin 38. The tongue portion 36 is further pulled toward the center axis, and at the same time, the bore 37 of the tongue portion 36 is fitted on the pin 33. Thus, the mounting of the blanket 30 requires much labor and time.
Furthermore, to form a clamping portion and a sealing portion in the radially outer portion of the end surface of the blanket-supporting disc 31, the blanket end portion devoid of cutouts is pulled up to the clamping and sealing portion, and in this state, the bores 37 of the tongue portions 36 are fitted on the pins 33. Therefore, that portion of the blanket where clamping and sealing are formed must be compressed in the circumferential direction. However, with the tongue portion 36 fixed by the pin 33, the blanket has an undulated portion between the root of the tongue portions 36. If the tongue portions 36 are fixed by the pins 33 over the blanket circumference, the pitch between the undulated portions becomes shorter. Therefore, the operation of forming undulated portions in the blanket end portion and also tensioning the tongue portions 36 and fixing the tensioned tongue portions 36 to the pins 33 requires much labor. This labor will be lessened if the roll diameter becomes greater. However, in the case where the roll diameter is small, the above-described operation is fairly difficult. The blanket is clamped and sealed when the undulated blanket end portion is forcibly deformed into a flat shape by clamping the clamping flange 32 to the supporting disc 31 with the mounting bolts. Because of this, residual stress occurs in the undulated portion and the blanket-mounting operation is not efficient.
The inner circumferential length of the blanket is made longer than the outer circumferential length of the supporting disk 31 to enhance the operation efficiency at the time of the blanket insertion. Because of this, even if the blanket is positioned at the tongue portions of the opposite end portions by employing the pins 33, bushes 41, and pins 38, the blanket hangs down below the blanket-supporting disc 31 by the flexibility and weight of the blanket itself. Therefore, even if the blanket is correctly positioned in the axial direction at the tongue portions, the blanket portion from the root of the tongue portion to the outer periphery of the supporting disk has already been twisted. That is, the centering of the blanket is insufficient. To avoid this problem, only an end portion of the blanket mounted on the outer periphery of the supporting disc without strain is loosely clamped at the uppermost portion of the roll. Thereafter, the blanket is rotated through about 180 degrees to move the lowermost portion to the uppermost portion. Next, only a blanket end portion correctly mounted on the outer periphery of the supporting disc is loosely clamped. After a sequence of these operations is repeated and temporal clamping is performed over the circumference, the blanket must be tightly clamped over the circumference. Furthermore, the clamping operation must be performed on both end portions of the blanket. Because of this, the clamping operation requires labor and time, and is not efficient.
The present invention has been made in view of the above-described problems. Accordingly, it is the object of the present invention to provide a press roll that has a high rate of operation, being capable of easily exchanging a flexible blanket in a short time.